Electrode, solid electrolyte electrolysis device, and synthetic gas production method

ABSTRACT

Techniques may relate to an electrode having high production efficiency of a synthetic gas containing at least CO. Such techniques relating to an electrode may include: a catalyst that produces at least carbon monoxide by a reduction reaction; an electrode material including the catalyst; and a solid base additive provided at least on the electrode material.

TECHNICAL FIELD

The present disclosure relates to an electrode capable of producing a synthetic gas containing at least carbon monoxide, a solid electrolyte electrolysis device, and a synthetic gas production method.

BACKGROUND ART

Fossil fuels (oil, coal, natural gas) support a modern energy consuming society. However, reserves of such fossil fuel are limited. Thus, various alternative fuels that will replace fossil fuels have been proposed. One of them is Hydrocarbon Fuel (HC). HC can be synthesized, for example, by subjecting a synthetic gas containing at least carbon monoxide (CO) and hydrogen (H₂) to Fischer-Tropsch reaction (FT reaction).

Patent Literature 1 proposes a synthetic gas synthesizing instrument. Specifically, an instrument is disclosed in which carbon dioxide (CO₂) is blown into seawater to lower the pH of the seawater from 8 to 5 to 6 in a tank provided separately from an electrolyzer, and the seawater after the pH adjustment is sent from the tank to the electrolyzer for electrolysis.

CITATION LIST Patent Literature

-   Patent Literature 1: JP 61-73893 A

SUMMARY OF INVENTION Technical Problem

The method of Patent Literature 1 has a problem of poor production efficiency of a synthetic gas due to the low solubility of CO₂ in water. Thus, an object of the present disclosure is to provide a technique related to an electrode having high production efficiency of a synthetic gas containing at least CO.

According to one aspect of the present disclosure, a technique including:

a catalyst that produces at least carbon monoxide by a reduction reaction;

an electrode material having the catalyst; and

a solid base additive provided at least on the electrode material can be provided.

Advantageous Effects of Invention

According to the present disclosure, a technique related to an electrode having high production efficiency of a synthetic gas containing at least CO can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a solid electrolyte electrolysis device suitably used in an embodiment of the present disclosure.

FIG. 2 is a conceptual diagram showing a situation where CO₂ can be efficiently adsorbed locally by addition of a solid base additive to a cathode surface in a solid electrolyte electrolysis device suitably used in an embodiment of the present disclosure.

FIG. 3 is a flowchart showing a synthetic gas production method in which a solid electrolyte electrolysis device suitably used in an embodiment of the present disclosure is used.

FIG. 4 illustrates use examples of a solid electrolyte electrolysis device suitably used in an embodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a solid electrolyte electrolysis device in the present disclosure will be specifically described with reference to one embodiment. The invention according to the present disclosure is not limited to the embodiment described below.

<<Solid Electrolyte Electrolysis Device 100>>

The solid electrolyte electrolysis device (also referred to as an electrolysis cell, an electrolysis module) according to the present embodiment will be described with reference to FIG. 1. As shown in FIG. 1, a solid electrolyte electrolysis device 100 according to the present embodiment includes a cathode (negative electrode) 101; an anode (positive electrode) 102 that constitutes a pair of electrodes with the cathode 101; a solid electrolyte 103 interposed between the cathode 101 and the anode 102 with at least a part of the solid electrolyte 103 being in contact with the cathode and the anode; a current collecting plate 104 in contact with a surface 101-2 that is opposite to a contact surface 101-1 with the solid electrolyte 103 of the cathode 101; a supporting plate 105 in contact with a surface 102-1 that is opposite to a contact surface 102-2 with the solid electrolyte 103 of the anode 102; and a voltage application part 106 that applies a voltage between the current collecting plate 104 and the supporting plate 105 (that is, between the cathode and the anode). By a supply source and a supply device (not illustrated), CO₂ in a gas phase and the supporting electrolyte H₂O are supplied. Though the solid electrolyte electrolysis device 100 illustrated in FIG. 1 is illustrated in a state where parts such as the cathode 101 and the anode 102 are separated from each other for explanation, actually, each of the current collecting plate 104, the cathode 101, the solid electrolyte 103, the anode 102, and the supporting plate 105 is bonded each other by a predetermined method and integrally configured. Each part can be removably assembled to constitute one solid electrolyte electrolysis device 100. Hereinafter, each component will be described in detail.

<Cathode 101>

(Reduction Reaction at Cathode 101)

The reduction reaction at the cathode 101 depends on the type of the solid electrolyte 103. When a cation exchange membrane is used as the solid electrolyte 103, reduction reactions of the following formulas (1) and (2) occur, and when an anion exchange membrane is used as the solid electrolyte, reduction reactions of the following formulas (3) and (4) occur.

Formula 1

CO₂+2H⁺+2e ⁻→CO+H₂O  (1)

2H⁺+2e ⁻→H₂  (2)

H₂O±CO₂+2e ⁻→CO+2OH⁻  (3)

2H₂O+2e ⁻→H₂+2OH⁻  (4)

(Basic Structure and Material of Cathode 101)

The cathode 101 is a gas diffusion electrode including a gas diffusion layer. The gas diffusion layer includes, for example, carbon paper or a nonwoven fabric, or a metal mesh. Examples of the electrode material of the cathode 101 include graphite carbon, glassy carbon, titanium, and SUS. The catalyst of the cathode capable of reducing CO₂ to CO included in the cathode 101 contains, for example, a metal selected from silver, gold, copper, or a combination thereof. More specifically, the catalyst includes, for example, gold, a gold alloy, silver, a silver alloy, copper, a copper alloy, or a mixed metal containing any one or more of them. The type of the catalyst is not particularly limited as long as the catalyst has a function as a catalyst, and can be determined in consideration of corrosion resistance and the like. For example, when the catalyst does not contain an amphoteric metal such as Al, Sn, or Zn, corrosion resistance can be improved. The catalyst can be supported on the cathode 101 (or the electrode material) by performing a known method such as vapor deposition, deposition, adsorption, sedimentation, adhesion, welding, physical mixing, and spraying.

(Solid Base Additive 107)

As shown in FIG. 2, the cathode 101 has a solid base additive 107. The solid base additive 107 is not particularly limited as long as the solid base additive 107 is a base that is solid at normal temperature (25° C.), and for example, potassium hydrogencarbonate (KHCO₃), sodium hydroxide (NaOH), an oxide of an alkaline earth metal, a hydroxide of an alkaline earth metal or a carbide of an alkaline earth metal {for example, magnesium oxide (MgO), magnesium hydroxide (Mg(OH)₂), magnesium carbonate (MgCO₃), calcium oxide (CaO), calcium hydroxide (Ca(OH)₂), calcium carbonate (CaCO₃), strontium oxide (SrO), strontium hydroxide (Sr(OH)₂), strontium carbonate (SrCO₃), barium oxide (BaO), barium hydroxide (Ba(OH)₂), barium carbonate (BaCO₃)}, an oxide of a rare earth metal, a hydroxide of a rare earth metal or a carbonate of a rare earth metal {for example, yttrium oxide (Y₂O₃) and lanthanum oxide (La₂O₃)}, hydrotalcite (for example, metal complex hydroacids, a carbonate, LDH, HT-CO₃, HT-OH), zeolite surface-treated with a base, a molecular sieve treated with a base, or porous alumina (KF—Al₂O₃) surface-treated with a base is preferably used. In particular, as described in Examples described later, a weakly basic solid base additive having a small atomic number is more preferable. An oxide of an alkaline earth metal, a hydroxide of an alkaline earth metal, or a carbide of an alkaline earth metal, an oxide of a rare earth metal, a hydroxide of a rare earth metal, or a carbonate of a rare earth metal, which are water-insoluble solid base additives, is further more preferably used because they are not flowed by water in a gas or water generated by a reaction, and durability of a cathode having the solid base additive 107 is not deteriorated. The term “water-insoluble” solid base additive refers to one having an insolubility in 100 mL of water at 20° C. of less than 10 mg. The solid base additive 107 is suitably present on a side of the contact surface 101-1 with the solid electrolyte 103 of the cathode 101. The reason for such a configuration is that the interface between the cathode 101 and the solid electrolyte 103 is a reaction site. The solid base additive 107 can be present as a mixture with the material of the cathode 101, or can be present in an integrated state as a compound. The solid base additive 107 can be supported on the cathode 101 (or electrode material) by performing a known method such as application, vapor deposition, deposition, and physical mixing. The mass per unit area of the solid base additive is not particularly limited, and is, for example, 0.1 to 10 mg/cm², and preferably 0.1 to 6 mg/cm².

The following mechanism of action is presumed to be the reason why the efficiency is increased when the solid base additive 107 is used. For example, when a gas having a low concentration of CO₂ of 10 to 20% such as an exhaust gas in a factory is supplied to the solid electrolyte electrolysis device 100, CO₂ is less likely to be adsorbed on the surface of the cathode 101 because of its low concentration. Thus, as shown in FIG. 2, it is understood that by adding the solid base additive 107 to the surface of the cathode 101, CO₂ can be efficiently adsorbed locally to a place where the solid base additive is present, and CO₂ reduction can be advanced. It is also understood that when a cation exchange membrane is employed as the solid electrolyte 103, CO₂ cannot be sufficiently adsorbed if the surface of the cathode 101 has a large amount of H⁺. In such a case, the reaction presumably proceeds when the solid base additive 107 is present (for example, the pH is preferably controlled to pH>2). Meanwhile, when an anion exchange membrane is employed as the solid electrolyte, CO₂ is adsorbed because OH⁻ is present on the cathode surface, which is suitable for CO₂ reduction. However, it is understood that when the amount of OH⁻ is too large, adsorption occurs in a state of stable CO₃ ²⁻ and the CO₂ reduction reaction does not sufficiently proceed. In such a case, the CO₂ reduction reaction presumably further proceeds when the weakly basic solid base additive 107 is present (for example, the pH is preferably controlled to pH<12). In the present invention, the electrode having such a solid base additive and catalyst can be expressed as “an electrode including a catalyst; an electrode material having the catalyst; and a solid base additive provided at least on the electrode material” (in other words, an electrode including an electrode material having a catalyst and a solid base additive), or “a cathode having a catalyst and further having a solid base additive” or the like.

<Anode 102>

(Oxidation Reaction at Anode 102)

The oxidation reaction at the anode 102 depends on the type of the solid electrolyte 103. When a cation exchange membrane is used as the solid electrolyte 103, the oxidation reaction of the following formula (5) occurs, and when an anion exchange membrane is used as the solid electrolyte 103, the oxidation reaction of the following formulas (6) occurs.

[Formula 2]

2H₂O→O₂+4H⁺+4e ⁻  (5)

4OH⁻→O₂+2H₂O+4e ⁻  (6)

(Basic Structure and Material of Anode 102)

The anode 102 is a gas diffusion electrode including a gas diffusion layer. The gas diffusion layer includes, for example, a metal mesh. Examples of the electrode material of the anode 102 include Ir, IrO₂, Ru, RuO₂, Co, CoO_(x), Cu, CuO_(x), Fe, FeO_(x), FeOOH, FeMn, Ni, NiO_(x), NiOOH, NiCo, NiCe, NiC, NiFe, NiCeCoCe, NiLa, NiMoFe, NiSn, NiZn, SUS, Au, and Pt.

<Solid Electrolyte 103>

The solid electrolyte 103 is interposed between the cathode 101 and the anode 102 with the solid electrolyte 103 being in contact with the cathode 101 and the anode 102. Though the solid electrolyte 103 is not particularly limited to a polymer membrane, a cation exchange membrane or an anion exchange membrane is suitable, and an anion exchange membrane is more suitable. As the cation exchange membrane, for example, a strongly acidic cation exchange membrane in which a sulfone group is introduced into a fluororesin base, Nafion 117, Nafion 115, Nafion 212 or Nafion 350 (manufactured by DuPont), a strongly acidic cation exchange membrane in which a sulfone group is introduced into a styrene-divinylbenzene copolymer base, or NEOSEPTA CMX (manufactured by Tokuyama Soda Co., Ltd.) can be used. Examples of the anion exchange membrane include an anion exchange membrane in which a quaternary ammonium group, a primary amino group, a secondary amino group, a tertiary amino group, or two of more of these ion exchange groups are present. As specific examples, for example, NEOSEPTA (registered trademark) ASE, AHA, AMX, ACS, AFN, and AFX (manufactured by Tokuyama Corporation), SELEMION (registered trademark) AMV, AMT, DSV, AAV, ASV, AHO, AHT, and APS4 (manufactured by AGC Inc.) can be used.

<Current Collecting Plate 104>

Examples of the current collecting plate 104 include metal materials such as copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, and brass, and among them, copper is preferable from the viewpoint of ease of processing and cost. When the current collecting plate 104 is a metal material, examples of the shape of the negative electrode current collecting plate include a metal foil, a metal plate, a metal thin film, an expanded metal, a punching metal, and a foamed metal.

As shown in FIG. 1, the current collecting plate 104 is provided with a gas supply hole 104-1 for supplying a gas and a gas collecting hole 104-2 for collecting a gas (raw material gas and produced gas) to the cathode 101. By the gas supply hole 104-1 and the gas collecting hole 104-2, the raw material gas can be uniformly and efficiently fed to the cathode 101 and the produced gas (including the unreacted raw material gas) can be exhausted. Though in this figure, one gas supply hole and one gas collecting hole are provided, the number, place, and size are not limited, and are appropriately set.

In addition, when the current collecting plate 104 has air permeability, the gas supply hole and the gas collecting hole are not necessarily required.

When the cathode 101 plays a role of transmitting electrons, the current collecting plate 104 is not necessarily required.

<Supporting Plate 105>

The supporting plate 105 supports the anode. Thus, the required rigidity of the supporting plate 105 changes depending on the thickness, rigidity and the like of the anode. The supporting plate 105 needs to have electrical conductivity to receive electrons from the anode. Examples of the material of the supporting plate 105 include Ti, SUS, and Ni.

As shown in FIG. 1, the supporting plate 105 is provided with a gas flow path 105-1 for feeding a raw material gas (H₂O and the like) to the anode 102. By the gas flow path, the raw material gas can be uniformly and efficiently fed to the anode 102. Though in this figure, eight gas flow paths are provided, the number, place, and size are not limited, and are appropriately set.

Though in the present embodiment, the anode 102 and the supporting plate 105 are described as separate structures, the anode 102 and the supporting plate 105 can be an integrated structure (that is, the anode 102 and the supporting plate 105 can be an integrated anode 102 having a support function).

<Voltage Application Part 106>

As illustrated in FIG. 1, the voltage application part 106 plays a role of applying a voltage between the cathode 101 and the anode 102 through application of a voltage to the current collecting plate 104 and the supporting plate 105. As described above, the current collecting plate 104 is a conductor, and thus feeds electrons to the cathode 101, while the supporting plate 105 is also a conductor, and thus receives electrons from the anode 102. When the current collecting plate 104 is not necessary as described above, a voltage is applied between the cathode 101 and the supporting plate 105. To apply an appropriate voltage, a control unit (not illustrated) can be electrically connected to the voltage application part 106.

<Reaction Gas Supply Part>

The solid electrolyte electrolysis device 100 in the present disclosure can be provided with a reaction gas supply part (not illustrated) outside the solid electrolyte electrolysis device 100. That is, it is sufficient that CO₂, a reaction gas, is supplied to the surface 101-2, and the reaction gas can be supplied from the reaction gas supply part to the gas supply hole 104-1 via a pipe (not illustrated) or the like, or the reaction gas can be blown to the surface 104-A of the current collecting plate 104 opposite to the contact surface 104-B with the cathode 101. A factory exhaust gas exhausted from a factory is suitably used as the reaction gas from an environmental viewpoint.

<<CO Production Method>>

A method for producing CO using the solid electrolyte electrolysis device 100 will be described with reference to FIG. 3.

<Reaction Gas Supply Step S301>

CO₂, a reaction gas, as a raw material is first supplied to the solid electrolyte electrolysis device 100 in a gas phase by a reaction gas supply part (not illustrated). At this time, CO₂ is supplied to the cathode 101 through the gas supply hole 104-1 provided in the current collecting plate 104 (S301).

<CO, H₂ Production Step S302>

Then, the CO₂ supplied to the cathode 101 undergoes reduction reactions on the surface of the cathode 101: when a cation exchange membrane is used as the solid electrolyte 103, the reduction reactions of the formulas (1) and (2) described above occur, and when an anion exchange membrane is used as the solid electrolyte, the reduction reactions of the formulas (3) and (4) described above occur. Thereby a synthetic gas containing at least CO and H₂ is produced (S302).

<Produced Gas Collecting Step S303>

Then, the produced synthetic gas containing CO and H₂ is sent to a gas collecting device (not illustrated) through a gas collecting hole 104-2 provided in the current collecting plate 104, and is collected for each predetermined gas (S303).

<<Use>>

As shown in FIG. 4, for example, by using CO₂ gas exhausted from a factory as a raw material and utilizing renewable energy of a solar cell or the like to the voltage application part 106 in the solid electrolyte electrolysis device according to the present disclosure as described above, a synthetic gas containing at least CO and H₂ can be produced at a desired production rate. From the synthetic gas thus produced, fuel base materials and chemical raw materials can be produced by techniques such as FT synthesis or methanation.

Examples

Hereinafter, specific description will be given with reference to Examples and Comparative Examples in which the present embodiments described above is used.

The solid electrolyte electrolysis device 100 shown in FIG. 1 was assembled (supporting plate=Ti plate of 3 mm), and the synthetic gas production results for each cathode catalyst and solid base additive material used were shown in Table 1 to 3.

TABLE 1 Effect of base addition on Ag catalyst (when anion exchange membrane is used) Partial Partial current current density density Material of FE (%) FE (%) (mA/cm²) (mA/cm²) solid base of H₂ of CO of H₂ of CO Judgement Judgement No addition  3.19 57.62 0.33  6.05 — Criteria 1 Example 1 KHCO₃ 26.87 54.28 3.07 6.2 Δ Example 2 MgO 20.85 77.19 2.72 10.08 ⊚ Example 3 Sr (OH)₃  4.15 54.61 0.71  9.28 ⊚ Example 4 BaCO₃ 26.36 58.17 3.81  8.25 ◯ Example 5 Y₂O₃ 23.51 58.78 3.43  8.58 ◯ Example 6 La₂O₃ 8.4 64.09 0.88  7.57 ◯

Table 1 shows experimental data in the solid electrolyte electrolysis device 100 when an anion exchange membrane was used as the solid electrolyte 103, silver (Ag) was used as a cathode catalyst, and each solid base additive was added to the cathode 101.

For experimental conditions in Table 1, a platinum mesh was used as an anode material, carbon paper on which Ag was applied to form a thin film was used as a cathode material, a saturated aqueous KHCO₃ solution was used as an anode electrolysis solution, and an applied voltage applied to the current collecting plate 104 and the supporting plate 105 was 3.5 V. The solid base additive was added so that the mass per unit area would be about 5.33 mg/cm².

The evaluation of the experimental results was performed as follows: the measured value of the partial current density (mA/cm²) of CO when no solid base additive was added was used as a judgment criteria, a symbol of Δ was given to a result in which an improvement of 2% or more was observed, a symbol of ∘ was given to a result in which an improvement of 10% or more was observed, and a symbol of ⊙ was given to a result in which an improvement of 50% or more was observed compared to the measured value, and those conditions that had such results were judged to be capable of improving the production efficiency of a synthetic gas (particularly, CO). The partial current density is a physical quantity representing the amount of electrons used to produce a specific compound, and the larger the value, the larger the production amount.

In Judgment Criteria 1 in which no solid base additive was added (no addition case), the partial current density of CO was 6.05 mA/cm². The Faraday Efficiency (FE) of H₂ was 3.19%, the FE of CO was 57.62%, and the partial current density of H₂ was 0.33 mA/cm². In this experiment in which an anion exchange membrane was used, these measured values were used as reference values for judgement.

In Example 1 in which KHCO₃ was added, the FE of H₂ was 26.87%, the FE of CO was 54.28%, the partial current density of H₂ was 3.07 mA/cm², and the partial current density of CO was 6.2 mA/cm². Thus, in Example 1, the partial current density of CO increased by about 2.5% compared to that of Judgment Criteria 1, and the production efficiency of CO was not significantly improved. This is presumably because KHCO₃ is water-soluble and was dissolved in H₂O produced by the reaction in the cathode, so that a sufficient base effect was not obtained.

Then, in Example 2 in which MgO was added, the FE of H₂ was 20.85%, the FE of CO was 77.19%, the partial current density of H₂ was 2.72 mA/cm², and the partial current density of CO was 10.08 mA/cm². Thus, in Example 2, the partial current density of CO increased by about 66.6% compared to that of Judgment Criteria 1, and the production efficiency of CO was successfully improved.

Then, in Example 3 in which Sr(OH)₂ was added, the FE of H₂ was 4.15%, the FE of CO was 54.61%, the partial current density of H₂ was 0.71 mA/cm², and the partial current density of CO was 9.28 mA/cm². Thus, in Example 3, the partial current density of CO increased by about 53.4% compared to that of Judgment Criteria 1, and the production efficiency of CO was successfully improved.

Then, in Example 4 in which BaCO₃ was added, the FE of H₂ was 26.36%, the FE of CO was 58.17%, the partial current density of H₂ was 3.81 mA/cm², and the partial current density of CO was 8.25 mA/cm². Thus, in Example 4, the partial current density of CO increased by about 36.4% compared to that of Judgment Criteria 1, and the production efficiency of CO was successfully improved.

Then, in Example 5 in which Y₂O₃ was added, the FE of H₂ was 23.51%, the FE of CO was 58.78%, the partial current density of H₂ was 3.43 mA/cm², and the partial current density of CO was 8.58 mA/cm². Thus, in Example 5, the partial current density of CO increased by about 41.8% compared to that of Judgment Criteria 1, and the production efficiency of CO was successfully improved.

Then, in Example 6 in which La₂O₃ was added, the FE of H₂ was 8.4%, the FE of CO was 64.09%, the partial current density of H₂ was 0.88 mA/cm², and the partial current density of CO was 7.57 mA/cm². Thus, in Example 6, the partial current density of CO increased by about 25.1% compared to that of Judgment Criteria 1, and the production efficiency of CO was successfully improved.

TABLE 2 Effect of base addition on Cu and Ag catalyst (when cation exchange membrane is used) Partial Partial current current Production Negative density density activity electrode Material of (mA/cm²) (mA/cm²) (μmol/h) catalyst solid base of H₂ of CO of CO Judgement Judgement Cu No addition 711 0   0   — Criteria 2 Example 6 Cu KHCO₃ 653 2.4 0.2 ◯ Example 7 Cu NaOH 635 16.7  1.4 ◯ Example 8 Cu La₂O₃ 622 66.7  5.6 ⊚ Judgement Ag No addition 763 0   0   — Criteria 3 Example 9 Ag La₂O₃ 610 32.2  2.7 ◯

Table 2 shows experimental data in the solid electrolyte electrolysis device 100 when a cation exchange membrane (Nafion 117) was used as the solid electrolyte 103, copper (Cu) or (Ag) was used as a cathode catalyst, and each solid base additive was added to the cathode 101.

For experimental conditions in Table 2, a platinum mesh was used as an anode material, carbon paper on which Ag was applied to form a thin film was used as a cathode material, 0.1 mol/L of sulfuric acid was used as an anode electrolysis solution, and an applied voltage applied to the current collecting plate 104 and the supporting plate 105 was 5 V. The solid base additive was added so that the mass per unit area would be about 5.33 mg/cm².

The evaluation of the experimental results was performed as follows: the measured value of the production amount (μmol/h) of CO per hour when the cathode catalyst was Cu and no solid base additive was added was used as Judgment Criteria 2, the measured value of the production amount (μmol/h) of CO per hour when the cathode catalyst was Ag and no solid base additive was added was used as Judgment Criteria 3, and those conditions that had results of larger production of CO than the measured values were judged to be capable of improving the production efficiency of CO.

In Judgment Criteria 2 in which Cu was used as a cathode catalyst and no solid base additive was added (no addition case), the production activity of CO was 0 μmol/h.

Then, in Example 6 in which Cu was used as a cathode catalyst and KHCO₃ was added, the production activity of CO was 0.2 μmol/h, and the production efficiency of CO was successfully improved.

Then, in Example 7 in which Cu was used as a cathode catalyst and NaOH was added, the production activity of CO was 1.4 μmol/h, and the production efficiency of CO was successfully improved.

Then, in Example 8 in which Cu was used as a cathode catalyst and La₂O₃ was added, the production activity of CO was 5.6 μmol/h, and the production efficiency of CO was successfully improved.

Then, in Judgment Criteria 3 in which Ag was used as a cathode catalyst and no solid base additive was added (no addition case), the production activity of CO was 0 μmol/h.

Then, in Example 9 in which Ag was used as a cathode catalyst and La₂O₃ was added, the production activity of CO was 2.7 μmol/h, and the production efficiency of CO was successfully improved.

Table 3 shows experimental data in the solid electrolyte electrolysis device when an anion exchange membrane was used as the solid electrolyte, a cathode catalyst (Cu—In) was used, and a MgO solid base additive was added to the cathode.

TABLE 3 Partial Partial current current density density Solid FE (%) FE (%) (mA/cm²) (mA/cm²) Catalyst base of H2 of CO of H2 of CO Judgement Judgement CU-In No addition 32 16 4.49 1.89 — Criteria 3 Example 1 CU-In MgO 56 59 4.50 2.40 ∘

For experimental conditions, a platinum mesh was used as an anode material, carbon paper on which a thin film of Cu—In was formed in a surface region was used as a cathode material, a saturated aqueous KHCO₃ solution was used as an anode electrolysis solution, and a voltage applied to the current collecting plate and the supporting plate were 3.5 V. The solid base additive was added in an amount of 5 mg/cm².

For a Cu—In catalyst, when a MgO solid base additive was added, the partial current density of CO increased by 26% compared to no addition case. The effect of base addition is sufficient. 

1. An electrode, comprising: a catalyst suitable to produce at least carbon monoxide by a reduction reaction; an electrode material comprising the catalyst; and a solid base additive provided at least on the electrode material.
 2. The electrode of claim 1, wherein the electrode is a cathode.
 3. The electrode of claim 1, wherein the solid base additive is an oxide of an alkaline earth metal, a hydroxide of an alkaline earth metal, a carbide of an alkaline earth metal, an oxide of a rare earth metal, a hydroxide of a rare earth metal, or a carbonate of a rare earth metal.
 4. A solid electrolyte electrolysis device, comprising: a cathode comprising a catalyst suitable to produce at least carbon monoxide by a reduction reaction; an anode that constitutes a pair of electrodes with the cathode; a solid electrolyte interposed between the cathode and the anode with the solid electrolyte being in contact with the cathode and the anode; and a voltage application part configured to apply a voltage between the cathode and the anode, wherein the cathode further comprises a solid base additive.
 5. The device of claim 4, wherein the solid base additive is present on a side of a contact surface with the solid electrolyte of the cathode.
 6. The device of claim 4, wherein the solid base additive is an oxide of an alkaline earth metal, a hydroxide of an alkaline earth metal, a carbide of an alkaline earth metal, an oxide of a rare earth metal, a hydroxide of a rare earth metal, or a carbonate of a rare earth metal.
 7. The device of claim 4, wherein the solid electrolyte is an anion exchange membrane.
 8. The device of claim 4, wherein the solid electrolyte is a cation exchange membrane.
 9. A synthetic gas production method, comprising: supplying a reaction gas to a solid electrolyte electrolysis device comprising a cathode comprising a catalyst, an anode that constitutes a pair of electrodes with the cathode, a solid electrolyte interposed between the cathode and the anode with the solid electrolyte being in contact with the cathode and the anode, and a voltage application part configured to apply a voltage between the cathode and the anode, wherein the cathode further comprises a solid base additive; producing a synthetic gas comprising carbon monoxide by a reduction reaction caused by the reaction gas being brought into contact with the cathode; and collecting the synthetic gas.
 10. The electrode of claim 2, wherein the solid base additive is an oxide of an alkaline earth metal, a hydroxide of an alkaline earth metal, a carbide of an alkaline earth metal, an oxide of a rare earth metal, a hydroxide of a rare earth metal, or a carbonate of a rare earth metal.
 11. The device of claim 5, wherein the solid base additive is an oxide of an alkaline earth metal, a hydroxide of an alkaline earth metal, a carbide of an alkaline earth metal, an oxide of a rare earth metal, a hydroxide of a rare earth metal, or a carbonate of a rare earth metal.
 12. The device of claim 5, wherein the solid electrolyte is an anion exchange membrane.
 13. The device of claim 6, wherein the solid electrolyte is an anion exchange membrane.
 14. The device of claim 11, wherein the solid electrolyte is an anion exchange membrane.
 15. The device of claim 5, wherein the solid electrolyte is a cation exchange membrane.
 16. The device of claim 6, wherein the solid electrolyte is a cation exchange membrane.
 17. The device of claim 11, wherein the solid electrolyte is a cation exchange membrane. 